The present invention related generally to methods and compositions for controlling aquatic weeds, and certain particular embodiments, methods and compositions for selectively controlling weeds such as hydrilla or watermilfoil utilizing a combination including penoxsulam or another ALS inhibitor herbicide and endothall.
As further background, aquatic plants very commonly arise as undesired weeds in waters and wetlands in the United States of America and elsewhere. Two such exotic weeds are hydrilla and watermilfoil, including Eurasian watermilfoil, which present problems in ponds, lakes, and other water bodies. The treatment of such bodies of water to eliminate or control the undesired or exotic aquatic weeds is often complicated by the fact that the agent used to control the undesired weed also can detrimentally affect the health of other, desirable or native plant life within the water body. Aquatic herbicides need to be in contact with submersed plants for a period of time (exposure time), which is dependent on the individual agent and the concentration at which it is used. Additionally, specific herbicides can require long exposures (months) to control certain plants in water, which can also cause increased detriment to non-target species. Furthermore, long exposures can be difficult to maintain in a fluid environment. Insufficient exposure can lead to poor efficacy or failed treatments. Thus, methods or techniques to reduce exposure times and/or reduce the concentrations of agents used to control submersed weeds could benefit efficacy and/or selectivity. Also, relying on a single herbicide mode of action can enhance the risk of selecting a resistant plant biotype to that particular agent. Thus, treatment regimens that are more selective for the undesired plant species, minimize potential for resistance development, and reduce exposure times are needed.
The efficacy and application rate of herbicidal agents against the target aquatic weeds depends on several factors, including, the specific formulation, the plant type, climatic conditions, water and sediment conditions in the water body, herbicide exposure time, and the like. At times, an inability to control an undesired plant can be eliminated simply by increasing the rate of application for a particular herbicidal agent. However, this is not always the case, and higher rates of application can exacerbate undesired affects on beneficial plants and aquatic organisms, and may not adequately compensate for insufficient exposure with the targeted plant.
One possible way to improve aquatic weed control is to combine two or more active compounds as part of a treatment program. However, the use of two or more active compounds often fails due to physical or biological incompatibility, lack of stability in co-formulation, decomposition of the compounds, antagonistic effects between the compounds, cost, and/or other factors.
In view of the background in aquatic weed control, the discovery of enhanced or alternative methods and compositions for the control of aquatic weeds has been a difficult endeavor. Serious needs thus remain.